In order to promote miniaturization and weight reduction of mobile devices, automobiles, etc., electric wires to be used for these applications are required to have their diameters reduced. Accordingly, it is required to form a covering layer made of an 15 insulating material covering the core wire (i.e. the inner conductor), with a thin thickness.
Heretofore, a liquid insulating varnish having a thermosetting resin dissolved in a solvent has been used for producing an enamel wire to be used for a winding wire. In order to produce an enamel wire by using the liquid insulating varnish, a core wire is 20 immersed in and coated with the liquid insulating varnish, which is then baked and thermally cured to form a covering layer. In such a case, it is possible to reduce the thickness of the covering layer e.g. by adjusting the concentration of the thermosetting resin in the liquid insulating varnish. In recent years, in order to increase productivity, a polyimide composition containing a photocurable polyimide has been proposed as a 25 liquid insulating varnish in Patent Document 1.
On the other hand, in the case of an electric wire other than a winding wire, a core wire is usually covered by extrusion molding a thermoplastic resin. In Patent Document 2, a tetrafluoroethylene/perfluoro(alkyl vinyl ether) copolymer, which is a fluorinated resin having a low relative dielectric constant and capable of being thinned, has been proposed in order to suppress a transmission loss.